PROJECT 3: Genetic Models for the Study of Fibrinolysis in Atherosclerosis Atherosclerotic vascular disease is the leading cause of morbidity and mortality in the US. Alterations in fibdnolytic activity may affect atherosclerosis through a variety of mechanisms. During the previous funding cycle of this award, we have demonstrated that deficiency of plasminogen activator inhibitor-1 (PAl-l), a key regulator of fibrinolytic activity, was associated with reduced murine atherosclerosis at arterial bifurcation sites suggesting that the fibrinolytic system may play a particularly important role at sites of turbulent flow. In the process of determining functional requirements for PAl-1 in vascular disease we have also investigated the role of vitronectin, an abundant glycoprotein which binds and stabilizes PAl-1. To our surprise, mice lacking vitronectin developed markedly accelerated atherosclerosis. The current grant proposal will expand on these initial observations by exploring potential mechanisms behind these findings and establishing the relevant tissue sources for PAl-1 and vitronectin in atherosclerosis. The effect of more modest changes in PAl-1 expression on atherosclerosis will be determined by analyzing atherosclerosis in mice with heterozygous PAl-1 deficiency and mice overexpressing PAI-I. Mice with tissue-specific PAl-1 expression will be generated to determine the relevant tissue compartments responsible for the observed effect of PAl-1 deficiency in atherosclerosis and thrombosis. Since PAl-1 may affect atherosclerosis by inhibition of uPA or tPA, we will assess the effect of uPA and tPA deficiency on atherosclerosis. We will further examine the role of fibrin clearance as the mechanism by which PAl-1 influences atherosclerosis by analyzing mice with combined PAl-1 and fibrinogen deficiencies. To further explore the proatherogenic effect of vitronectin deficiency, aortic transplantation experiments between mice with and without vitronectin will be performed to determine the effect of local vascular wall vitronectin expression on atherogenesis. Further information regarding the pathway by which vitronectin influences atherosclerosis will be obtained by assessing atherosclerosis in mice deficient in the vitronectin receptor, O_vP3. The results of these studies will clarify the role of fibrinolysis in atherosclerosis and the studies with vitronectin deficient mice may provide clues to novel pathways involved in atherogenesis which could lead to new treatment strategies.